We propose that cultured skin fibroblasts from patients with protoporphyria can be used to investigate the abnormality in protoporphyrin metabolism which characterizes this genetic disorder. We have made the preliminary observation that fibroblast sonicates of these patients have a deficiency of heme synthetase activity. A defect in this enzyme, which catalyzes the chelation of iron to the protoporphyrin molecule to form heme, could cause the protoporphyrin overproduction observed in this disease. Further studies will be done to characterize the nature of the deficient heme synthetase activity, using mixing studies with control and protoporphyric fibroblast sonicates, and by performing Michaelis-Menten analysis with partially-purified enzyme. The genetic hypothesis that this is a dominant trait will be examined by measuring heme synthetase activity in fibroblast sonicates from parents of affected individuals. Parallel studies will be done to determine if protoporphyric fibroblasts will accumulate protoporphyrin under certain incubation conditions, as this would allow us to examine the effect of protoporphyrin accumulation at a cellular level. If is can be shown that protoporphyric cells accumulate significantly more protoprophyrin than non-porphyric cells, the dominant nature of protoporphyria will also be examined in somatic cell hybrids.